Solvent Dependency in the Synthesis of Multiblock and Cyclic Poly(2-oxazoline)s

Multiblock copolymers as well as cyclic polymers exhibit unique physical properties and are being utilized in various applications. However, the synthesis of such polymers is quite challenging because there is a delicate balance in achieving either structure. Here, we report a surprising solvent dependence on the cyclization and step-growth reactions of poly(2-alkyl 2-oxazoline)s. Additionally, other important parameters such as catalyst concentration, polymer concentration, and temperature were investigated, and their influences on the obtained ratio between step-growth and cyclization polymers are discussed. Step growth of a telechelic poly(2-ethyl 2-oxazoline) macromonomer yielded a multiblock polymer containing, on average, eight repeating units. Moreover, reaction conditions in order to favor cyclization over step-growth polymerization were optimized for poly(2-fatty acid-2-oxazoline). Finally, using the optimized conditions, an up to 80:20 cyclization/step-growth polymer mixture was obtained at a relatively high polymer concentration (50 mg/mL).